The invention relates to a communication system for data interchange in a technical automation installation for communication between central and peripheral devices.
It is known for so-called fieldbus systems to be used for communication purposes at the field level in a technical automation installation. In field bus systems, the measured values are digitized in the field device or in local I/O assemblies, and then supplied via a field bus network to a higher-level controller. At least one communication link and the feed for the assembly are required for this purpose.
There are bus systems in which the feed and communication can take place via one and the same pair of conductors (for example PROFIBS PA, Foundation Field Bus).
Because of the network structure, all the field devices are galvanically connected to the field bus network. A disturbance affecting only one subscriber therefore affects the entire network. Data transmission is therefore likewise no longer possible for all the other subscribers, or is subject at least to considerable interference. In the extreme, the disturbance can lead to considerable, irreparable damage. Typical disturbances in technical process installations include in particular shorts, line discontinuities, electromagnetic interference and lightning strikes.
Furthermore, deliberate actions by the operator on a technical automation component can also be regarded as disturbances. These actions are, for example, required for maintenance purposes and in this case always represent a risk to the continuous operation of an installation that is required in the process industry. This includes, in particular, upgrades to the functional scope of a technical automation installation, for example as required for integration of installation management systems.
Installation management systems such as these are used to gather and process information relating to the status of the peripheral appliances. The central controller for a technical automation installation is designed primarily for processing process values, and is also unsuitable for obtaining and producing information such as this from peripheral appliances which are connected in an analogous form via a 0/4 . . . 20 mA interface. This relates in the same manner to process controllers with analogue information transmission and superimposed HART communication, in which the input/output assemblies are not suitable for connection of the peripheral appliances for HART communication, as well as a field bus system without acyclic services. In these process controllers, the information required for installation management is not available in the central controller and is therefore not accessible by a higher-level installation management system.
It is known from the publication “H.I.S. HART INTERFACE SOLUTIONS”, Part. No. 475215, from the Pepperl+Fuchs Company for so-called multiplexer solutions to be used to provide the asset management information for HART-compatible appliances. These multiplexer solutions are installed in the communication path, in order to pass the desired information beyond the central controller. However, retrospective installation is a significant action which virtually always leads to connection of the installation. Actions such as these in the structure of the communication path are often also undesirable because they are associated with a large amount of documentation and test effort or because the space for the additionally required components along the communication path is not available, or its provision would be extremely costly.
A further disadvantage of multiplexer solutions is the frequently undesirable coupling between installation topology and the installation management topology. For example, it is normally impracticable to use only individual signals to provide the installation management information with one multiplexer, since the wiring of the multiplexers follows the normal eight-channel or sixteen-channel implementation of an input/output assembly. This disadvantage also applies to input/output assemblies for connection of the peripheral appliances which are suitable for HART communication, and to fieldbus systems with acyclic service support.
The article “Das drahtlose Sensornetzwek” [The wireless sensor network], published in the 2005 Sensor Guide in Computer & AUTOMATION, pages 14 to 18, discloses sensor signals being transmitted without the use of wires and possibly via a plurality of sensor nodes. The process values are disadvantageously no longer available in analogue form or as a bus signal. In this case, however, cable supply lines are still required for the power supply. The alternative power supply using batteries or solar cells requires a very large amount of maintenance effort and/or is dependent on the weather, and is therefore unacceptable to operators of technical automation installations.
Furthermore, bus systems are known in which optical waveguide paths or radio links are used for signal transmission between two devices connected on a 1:1 basis. The assemblies which are distributed in the panel are still connected conventionally via galvanically coupled bus networks.